1. Field of the Invention
The present invention relates to a method for forming cavity patterns (a series of hollowed out spaces) in a glass layer. More particularly, the present invention relates to a method involving chemically etching a foam glass layer applied to a substrate to form cavity patterns in the foam glass layer. Most particularly, the present invention relates to a method which results in anisotropic etching of a foam glass layer to form cavity patterns therein. The present invention also relates to articles having cavity patterns formed in the foam glass layer through the utilization of the chemical etching process.
2. Background of the Invention
Glass layers are often coated onto various substrates and subsequently patterned, using various techniques, to provide functional or aesthetic patterns in the glass. An example of patterned glass layers is the use of channeled glass material as a barrier rib on plasma display panels.
Plasma display panels are often utilized as video display panels for devices such as televisions and monitors. The construction of plasma display panels includes generally sheet-like front and back glass substrates having inner surfaces that oppose each other with a chemically stable gas hermetically contained between the panels by a seal. The seal is positioned between the substrates at the periphery of the panel. Elongated electrodes covered by a dielectric layer are provided on both substrates, with the electrodes on the front glass substrate extending transversely to the electrodes on the back glass substrate. The electrodes define gas discharge cells or pixels that can be selectively energized by an electric driver of the plasma display panel.
The panels are generally provided with phosphors to enhance the luminescence and, thus, the efficiency of energizing the panels. The phosphors can also be arranged in pixels having at least three subpixels or gas discharge cells for respectively emitting the primary colors to provide a full color plasma display.
The conventional construction of back glass substrates for plasma display panels has elongated gas discharge cavities or troughs, and corresponding barrier ribs that separate the troughs from each other. The spaced apart troughs form isolated columns of pixels.
Each column of pixels is thereby isolated from the column on either side of the trough. The isolation of the columns of pixels provides good color separation and pixel definition. Other construction geometries employing more complex cavity patterns than channels have also been used, such as waffle patterns, diamond patterns, egg crate or honeycomb patterns, etc. All of the various patterns in totality shall henceforth be referred to as the cavity patterns; and all contain some type of walled structure, generally along the sides or perimeter of the cavity, that shall henceforth be referred to as the barrier rib.
There are several methods utilized to form the gas discharge cavity pattern and barrier rib construction in the glass layer. The barrier ribs are generally formed through either some type of direct printing or pressing process, or the casting or transferring of a full layer, followed by the removal of a portion of the layer to create the rib structure. In the latter, the removal of a portion of the layer to create a cavity pattern is accomplished by one of several practices including development of the unwanted material if the full layer contains a photosensitive component.
In the case of direct printing by a screen printing technique, a dielectric paste is printed between electrodes to form the barrier rib structure. The paste is printed between the electrodes using a screen pattern. One or more glass compositions and one or more firing cycles may be used to build the barrier rib to a desired height, and thus form a cavity pattern of a desired depth. This method can create quality issues as a result of alignment of the pattern in multiple printings. The printing technique is also difficult to apply to large areas, and can result in resolution limitations.
Another approach in forming gas discharge barrier ribs is to photolithographically form a resist layer on the prefired frit surface, in which the areas to be removed are exposed. The exposed areas are subsequently sandblasted to abrasively remove the glass frit and provide the barrier structure. Typically, an initial dielectric layer is applied over the electrode pattern prior to application of the glass barrier material. The initial dielectric layer is cured at a higher temperature than the barrier rib firing (or sintering) temperature and is applied to protect the electrodes during sandblasting. The glass barrier layer is applied by a suitable process such as screen printing and partially fired to provide the strength needed for the subsequent processing. A resist mask is then formed to both protect and expose those regions of the partially fired barrier material. The layer is subsequently sandblasted to form the barrier structure. The barrier ribs formed by the sandblasting are then fired at high temperature to sinter the glass particles comprising the barrier rib. The sandblasting process is dirty and expensive.
The barrier rib structure may also be created in the glass layer by chemically etching a vitreous glass layer using conventional photolithographic techniques to form a photoresist mask similar to that utilized in the sandblasting method. The exposed areas are then etched to create the cavity pattern and barrier ribs. One of the limitations of the conventional etching process is the effective isotropic nature of the etching, i.e. that the lateral etch rate is equal to the vertical etch rate. This limits the ability to form deep cavity patterns at high resolutions.
It would be an advantage to provide a method for creating deep cavity patterns in a glass barrier layer that utilizes effective anisotropic etching of the glass barrier layer. It would also be an advantage to provide a method for creating barrier ribs that does not adversely affect the substrate or require a separate dielectric layer to protect the electrodes.
The present inventive method involves the chemical etching of a foam glass layer to provide at least one cavity pattern in the foam glass layer. The etching of a foam layer results in an anisotropic etch rate. An anisotropic etch rate indicates that the etching in the vertical direction occurs at a rate that is greater than the etching rate in the horizontal or lateral direction.
The method of forming cavity patterns in a foam glass layer includes providing a substrate with at least one major surface suitable for receiving a glass layer. At least one layer of a glass paste composition is then applied onto the major surface of the substrate. The substrate and glass paste composition are then heated in at least one firing cycle to a temperature sufficient enough to obtain a foam glass layer bonded to the major surface of the substrate. At least a portion of the foam glass layer is chemically etched to obtain at least one rib pattern in the foam glass layer.
In a preferred embodiment, the substrate is a glass substrate, and the foam glass layer is etched to provide barrier ribs that define gas discharge troughs in a plasma display panel. The etched cavity pattern can be simple straight channels or more complex geometric patterns such as waffle patterns, diamond patterns, egg crate or honeycomb patterns, etc. Cavity patterns are defined by and separated from each other by barrier rib structures having various possible cross-section profiles or shapes, such as modified I-beams or trapezoids. Electrodes are first deposited onto the glass substrate followed by application of a uniform glass dielectric which is fired prior to application of the foam barrier glass paste composition. After formation of the foam glass layer, channels are etched into the foam glass layer in a pattern defined by a photoresist. The channels are etched in the foam glass layer at locations that correspond to the position of the electrodes.
The resulting article is suitable for use as a back substrate in a plasma display panel in a preferred embodiment, but could be used as a front substrate in certain plasma display designs. Phosphors are then placed in the channels to enhance the luminescence from the gas discharge when the electrodes are activated. Phosphors may not be necessary if a monochrome display is desired.